1. Field of the Invention
This invention relates to an auxiliary power steering unit, especially for motor vehicles. Such an auxiliary power steering has a control valve--made as a rotary slide valve--for controlling a pressure medium that is conveyed to and from the pressure chambers of a servomotor from a tank by a servopump. The rotary slide valve has two feedback chambers that are connected to the pressure line of the servopump via one, each, fixed throttle and via one common throttle. The feedback pressure that takes effect in the feedback chambers is limited to a maximum value by means of at least one cutoff valve.
2. Description of the Prior Art
Such an auxiliary power steering is known from EP-B1-0198824.
If the cutoff valve mentioned in this publication is made in the form of a seat valve, which is frequently the case, then the pressure medium stream regulated upon the valve's response is diverted directly into the tank. As a result, the pressure medium volume that is available for the servomotor of the auxiliary power steering is reduced considerably. Besides, flow and oscillation noises are generated during the diversion of the pressure medium screen. The switching pressure is also tolerance-tainted by unavoidable production tolerances.
The purpose of the invention is so to improve an auxiliary power steering known according to the state of the art that one can most extensively prevent a loss of pressure medium upon response of the cutoff valve and that the tolerances of the response pressures of the cutoff valve can, if at all possible, be avoided entirely.